Sunday, May 23, 2010

In which the EPA explains to Judith Curry why Tom Segalstad is wrong, wrong, wrong.

Comment (2-3):Several commenters state that CO2 has a short lifetime in the atmosphere (0711.1, 0714.1): for example, a commenter (1616) claims that the lifetime of CO2 can be at most 20 years based on the 12% annual exchange of CO2 with the surface ocean and 10% exchange between the surface and deep ocean as shown in the National Aeronautics and Space Administration (NASA) carbon cycle diagram, and two commenters (3440.1, 3722) state that the overwhelming majority of scientific papers support a residence time of seven years in contrast to the TSD and IPCC. Several commenters (e.g. 3722) cite Professor Segalstad who has stated, based on his work on CO2 residence times (Segalstad 1997), that the assumption of a 50- to 200-year lifetime by IPCC results in a “missing sink” of 3 Gt of carbon a year, which is evidence that IPCC is mistaken.

Another commenter submitted Essenhigh (2009), which developed a box model and also found that the lifetime of CO2 was on the order of a few years.

Response (2-3):EPA reviewed the information presented, as well as the work by Segalstad, and finds that it does not address the lifetime of a change in atmospheric concentration of CO2, but rather the lifetime in the atmosphere of an individual molecule of CO2. These are two different concepts. As stated in the First IPCC Scientific Assessment, “The turnover time of CO2 in the atmosphere, measured as the ratio of the content to the fluxes through it, is about 4 years. This means that on average it takes only a few years before a CO2 molecule in the atmosphere is taken up by plants or dissolved in the ocean. This short time scale must not be confused with the time it takes for the atmospheric CO2 level to adjust to a new equilibrium if sources or sinks change.

This adjustment time ... is of the order of 50–200 years, determined mainly by the slow exchange of carbon between surface waters and the deep ocean” (Watson et al., 1990). The magnitudes of these large balanced sources and sinks are addressed in response 2-2, and are similar to those represented in the NASA carbon cycle diagram. Newer research has only extended and confirmed this statement from the first IPCC assessment report (Denman et al., 2007). A recent approximation for this perturbation lifetime is sometimes represented as the sum of decay functions with timescales of 1.9 years for a quarter of the CO2 emissions, 18.5 years for a third of the CO2, 173 years for a fifth of the CO2, and a constant term representing a nearly permanent increase for the remaining fifth (Forster et al., 2007).

The “missing sink” that was referred to by a commenter is also addressed in response 2-2, and is now called the “residual land sink.” The magnitude of this sink is about 2.6 Gt of carbon per year, with significant uncertainty. Denman et al. (2007) included a hypothesis that a portion of this sink is due to the increased growth of undisturbed tropical forest due to CO2 fertilization, but the carbon accumulation of natural systems is hard to quantify directly. The uncertainty in determining the size and nature of this residual sink does not contradict the assessment literature conclusions about the perturbation lifetime of CO2 concentration changes in the atmosphere, but is reflected in the carbon cycle uncertainty for future projections of CO2 (see responses regarding carbon cycle uncertainty in Volume 4 on future projections).

The box model in Essenhigh (2009) is clearly flawed: the results from this model as reported in the paper include a lifetime for CO2 containing the 14C isotope that is a factor of 3 different from the lifetime of CO2 containing the 12C isotope. This difference in lifetimes is not scientifically compatible with the immense difficulty involved in isotope separation. The model assumes that each “control volume” (each volume represents either the ecosystem, the surface ocean, or the deep ocean) is perfectly mixed, which is contrary to the observations of oceanic CO2 which show that storage of carbon in the ocean is only at 15% of the equilibrium value, and that the mixing time between the surface ocean and intermediate and deep oceans is on the order of years to centuries (Field and Raupach, 2004). Additionally, the paper uses only historical fossil fuel emissions of CO2, without including land use change CO2, and contains the same confusion about “residence lifetime” and “adjustment lifetime” that has been addressed above.

A common analogy used for CO2 concentrations is water in a bathtub. If the drain and the spigot are both large and perfectly balanced, then the time than any individual water molecule spends in the bathtub is short. But if a cup of water is added to the bathtub, the change in volume in the bathtub will persist even when all the water molecules originally from that cup have flowed out the drain. This is not a perfect analogy: in the case of CO2, there are several linked bathtubs, and the increased pressure of water in one bathtub from an extra cup will actually lead to a small increase in flow through the drain, so eventually the cup of water will be spread throughout the bathtubs leading to a small increase in each, but the point remains that the "residence time" of a molecule of water will be very different from the "adjustment time" of the bathtub as a whole.

This analogy does not hold for other GHGs: methane, HFCs, and N2O are actually destroyed chemically in the atmosphere, unlike CO2 where the carbon is not destroyed but merely shifted from one reservoir to another, and therefore the residence lifetime of these gases is fairly close to the adjustment lifetime of their concentrations in the atmosphere.

Similarly, any given molecule of CO2 is only expected to stay in the atmosphere for a few years before it moves into the oceans or ecosystem, but the change in atmospheric concentration due to combustion of fossil fuels can persist for much longer. Indeed, because the oceans and ecosystems are finite, some small fraction of CO2 emissions will have a perturbation lifetime in the atmosphere of thousands of years (Karl et al., 2009).

22 comments:

Anonymous
said...

Did the folks with EPA who had to wade through all this get some sort of special gift? I hope so; for the most part this work appears to have been akin to employing neurosurgeons to operate toilet plungers, not good for morale.

EliI've a few questions:a. How do you sensibly contruct a model of sinks when you don't know what or where half of them are?b. Is the fact that CO2 dissolves in rainwater included? I mention this because big play is made of the short residence time of water and I can't reconcile the two.c. Any guesses on where the missing sink is?d. How can you use a bathtub analogy when you don't know the size of the bath? eg Is the sea a full bath or a largely empty one?e. I read that the IPCC models use that simple bathtub analogy. True?f. Is this another "all other things being equal" model?, ie what we don't know is considered to be net neutral.

These EPA scientists should be nominated for sainthood. They show an incredible amount of patience and really go way beyond the call of duty.

And, with them as examples, I'll try to address a couple of jgdes's questions:

b. Is the fact that CO2 dissolves in rainwater included? I mention this because big play is made of the short residence time of water and I can't reconcile the two.

I imagine it is a fairly negligible effect. However, even if it weren't, the point is that this would just transfer the CO2 to another subsystem (mixing layer of ocean or soils or biosphere) with which the atmospheric CO2 already rapidly equilibrates. The problem is removing the carbon from the ocean mixed layer + biosphere + soils + atmosphere system (either by burial into the deep ocean or burial underground). It is that process that is the rate-limiting step.

d. How can you use a bathtub analogy when you don't know the size of the bath? eg Is the sea a full bath or a largely empty one?

I don't even know what this means. The bathtub is an analogy. Any analogy can be carried too far. The ocean uptake of CO2 is determined by the chemistry in the ocean. It is not literally a bathtub.

e. I read that the IPCC models use that simple bathtub analogy. True?

To do calculations? No...The IPCC uses carbon cycle models, of which I believe the very simplest is the sort of model described by the EPA scientists (i.e., different fractions of the CO2 having different exponential decay constants).

It seems like you are really, really desperate to continue believing what you want to believe.

"The results additionally support the outcomes of theanalytical extension that includes the effect of a rising inputflux rate (Fi) with time, with the further comparison that thisthen accounts for the Watson et al.3 “adjustment time” data rangeof 50-200 years (although in contradiction to their furtherinterpretation of that result as a RT)."

He tries to mess it up so he can say that the increase comes from natural sources after some time... where he comes with the it is the oceans that is warming and releasing CO2 absurdity. Now I don't know exactly how the curve for C13/C12 look however ignoring that C14 is not in isotopic equilibrium will shift it by a factor 10 or so... ad a few other oversimplifications and who knows :)

Some local deniers promoted the paper in absurdity so I have a few scores to settle when the response is published... do tell!

Magnus, I think Essenhigh's work is a sincere attempt to get to the truth as he sees it and where it is wrong it seems to me to be an honest misunderstanding of the carbon cycle. I wish he were right!

The key point is that the residence time depends on the magnitude of the environmental uptake flux, whereas the adjustment time depends on the net difference between total uptake and total emissions, and hence can't be adequately modeled by variable input flux. As the difference between fluxes is small in comparison to their magnitude, it is hardly surprising that the adjustment time is much longer than the residence time.

There are good solid arguments refuting the idea that the observed rise is anything other than anthropogenic at Ferdinand Engelbeens excellent website. The mass balance argument ought to be proof enough for any reasonable person.

Eli: Yes, indeed that is a pity, however we often learn most from our mistakes, so it may turn out to be a valuable experience in research in the long run.

Other then that the citation above and I just cant believe that e chemist honestly can believe that the CO2 is coming from the ocean while the pH is decreasing... also seams like he clearly are avoiding all other Isotope studies and so on...

The local (Swedish) deniers are not reasonable ppl... have written a lot abut them but almost always in Swedish.

However the right way to take it on might just bee treating it like a honest mistake any way. Just don't leave doors open for simple comebacks just stating that he know the difference between the RT and adjustment time and have proven the old theory wrong...

I don't think Spencer's model works at all. If only 10% of the increase in atmospheric CO2 is from anthropogenic sources, about 5 GtC/y is taken up by the biosphere (since Spencer claims the oceans are a source). More importantly, however, since the increase in atmospheric CO2 is about 2 GtC/y, 1.5 GtC/y would be coming from the oceans. Since there is no reason for the biosphere to not also take up 90% of the oceanic CO2 (apart from the small C12/C13 issue), this means the oceans are throwing out 13 GtC/y MORE than they take up. That's an enormous number, equalling about 15% of the estimate C-flux of the ocean (which is about 90 GtC/y).

Within a few years, the oceans would be depleted of carbon if Spencer is right. Doesn't quite fit the measurements (and I'm not just talking about decreasing pH).

Thanks, Magnus. It doesn't explain my first link, where Spencer makes this naive (and provingly idiotic) claim that the oceans are the cause by "modeling".

I also note now that I made a considerable underestimation of the amount Spencer (in essence) claims is emitted from the oceans.

Take a 2 GtC/y increase, 90% from the oceans (according to Spencer). Then of the 5.5 GtC/y of human emissions, 5.3 GtC/y is taken up (0.2 GtC/y goes into the atmosphere). That is equal to 4%, not the 10% I took earlier. In other words, the 1.8 GtC/y that comes out of the ocean and contributes to the atmospheric increase is only 4% of the net flux from the ocean. That would mean the oceans emit 45 GtC/y more than they take up. With an estimated upper ocean content of 1000 GtC, it would take a mere 20 years to deplete the upper ocean of carbon.

Spencer's own diagram shows the error in his argument, if the environment were a net source of CO2 then the annual increase in atmospheric CO2 would be greater than the level of anthropogenic emissions as you would have both man and nature making contributions. The fact that atmospheric growth is always smaller (if you include land-use changes as well), shows that the natural environment is a net sink, and hence is not the cause of the observed increases.

Having a model is all very well, but you do need to make sure that the results are sensible. In this case, the problem is that SST have a rising trend that acts as a proxy for (is correlated with) anthropogenic emissions. The regression gives greater weight to SST as it also explains the wiggle due to ENSO, and you then need less of the Anthropogenic CO2 signal to get the required trend. The use of regression type models is fraught with this kind of problem.

Unfortunately it seems the confused, stupid and just plain ignorant have decided that the Royal Society needs to re-write its stance on global warming. That is, the critiscisms that i've seen so far in the press, credited to anonymous Royal Society members, sound like the same emeritus ranting that we see all the time. Nevertheless they have managed to force the comments to be re-written.http://news.bbc.co.uk/1/hi/science_and_environment/10178124.stm

Its the usual creationist trick of claiming something which was never designed to be the last word on a topic does not properly distinguish between what is agreed and what is not fully understood.

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Eli Rabett

Eli Rabett, a not quite failed professorial techno-bunny who finally handed in the keys and retired from his wanna be research university. The students continue to be naive but great people and the administrators continue to vary day-to-day between homicidal and delusional without Eli's help. Eli notices from recent political developments that this behavior is not limited to administrators. His colleagues retain their curious inability to see the holes that they dig for themselves. Prof. Rabett is thankful that they, or at least some of them occasionally heeded his pointing out the implications of the various enthusiasms that rattle around the department and school. Ms. Rabett is thankful that Prof. Rabett occasionally heeds her pointing out that he is nuts.